A wheel is mounted on a spindle or steering knuckle. The spindle or steering knuckle includes support arms or extensions or portions for the reception of upper and lower ball joint assemblies. A ball joint is a ball and socket connection, and a ball stud extends from the ball portion of the ball joint.
An axle arm assembly, such as an I-beam axle arm assembly, includes a first or inner end anchored to the frame of the vehicle and a second or outer end supported by a coil spring and a radius arm. The second end is further engaged to the wheel by the upper and lower ball joint assemblies.
An upper portion of the second end of the axle arm assembly engages the stud of the ball of the upper ball joint. By manipulating the orientation of the upper portion of the second end of the axle arm relative to the stud of the ball of the ball joint, certain positions of the wheel relative to the frame of the vehicle may be adjusted. These certain positions are camber and caster.
Upper and lower steering pivot points, such as upper and lower ball joints, help define a caster angle. The upper and lower steering pivot points can be 1) the upper and lower ball joints of a wishbone suspension design, 2) the upper and lower ball joints of an A-arm suspension design, or 3) the lower ball joint and the strut tower mount of a McPherson strut design.
The caster or caster angle is the slope of a straight line running through the upper and lower steering pivot points relative to a vertical line running perpendicular to the ground and through the center point of the tire, when viewed from the side of the vehicle. Caster is a backward or forward tilt of a kingpin, ball joint, or strut at the top of the wheel assembly. A backward tilting is referred to as positive caster. A forward tilting is referred to as negative caster. Caster is a directional control angle or steering angle, not a tire wearing angle. Proper adjustment of the caster angle helps the front wheels maintain a straight ahead position or return to a straight ahead position out of a turn. Positive caster (a tilting back) places the point of load ahead of the wheel contact. Depending upon the vehicle, either positive or negative caster may be desired.
Camber is a tire-wearing angle. Camber, like caster, is a directional control angle. The camber or camber angle is the tilting of a front wheel relative to the vertical when viewed from the front of the vehicle. More specifically, camber is the inward or outward tilt of the wheel at the top relative to the ground or true vertical. Positive camber is the angle of the outward tilt relative to true vertical. Negative camber is the angle of the inward tilt relative to true vertical. By properly adjusting the camber angle, then 1) the road contact of the tire is brought more nearly under the point of load, and 2) easier steering is provided by allowing the weight of the vehicle to be carried by the inner wheel bearing and spindle.
One method of caster and camber adjustment includes the steps of removing the original or first bushing, temporarily installing a standard zero offset or second bushing, taking camber and caster readings with the temporary installed, standard zero offset or second bushing in place, removing the standard zero offset or second bushing, and then installing an after market or third bushing.